border-1px($color)
  position :relative
  &:after
    display :block
    position :absolute
    left:0
    bottom:0
    width:100%
    border-top :1px solid $color
    content :''
border-none()
  &:after
    display: none
bg-image($url)
  background-image :(url($url+"@2x.png"))
  @media (-webkit-min-device-pixel-ratio:3),(min-device-pixel-ratio:3)
    background-image :(url($url+"@3x.png"))
